The chemical analysis of trace quantities of toxic substances by gas chromatograph/mass spectrometer (GC/MS) instruments requires the concentration of those substances on a trap, and subsequent release of those substances into an analytical column to separate the substances from each other on the way to the mass spectrometer. The analytical column may be negatively affected by water. In this regard, water vapor is a major problem for GC/MS systems, and must be eliminated as much as possible from the sample being injected for analysis. Trace analysis requires the concentration of substances of interest from about a liter of gas (usually air or helium, if the sample is purged from contaminated soil or water). Currently, commercial purge and trap systems used to concentrate samples for trace analysis by GC/MS incorporate ‘water management’ systems to remove water with the objective of minimally affecting the sample. However, those systems still do not function perfectly, and they add an additional several minutes to the analytical time for every sample while they cycle to remove the water.
The drying of samples prior to concentration for GC/MS systems has been done previously in two ways. The first was the use of Nafion®, a polar polymer. Nafion® tubing passes water and some other polar substances through it, while being impervious to most nonpolar substances. Nafion® is currently used as the membrane in hydrogen fuel cells, with minor use as a dryer. In prior years, perhaps up to about 20 years ago, air samples were put through Nafion® tubing to remove the water. It worked well for a lot of compounds, but fell short for polar compounds. In experiments conducted in the late 1970's, about 70% of methanol and 30% of ethanol went through the Nafion® with the water, and was lost. It was tested and used by the EPA in its Method TO-14 to dry sample air as it was being pumped into a sample container to greater than atmospheric pressure. It worked well for a number of toxic substances, but many of the polar toxic substances were lost through the Nafion® to such a degree that the method was eventually replaced. Therefore, as the government expanded its list of target substances, and those compounds included some very polar substances, a new solution was found.
Method TO-15 uses samples collected in evacuated containers, and the sample pressure does not reach atmospheric pressure, to prevent water condensation. The sample pressure is then measured, and the sample container pressurized with inert, dry gas to above atmospheric pressure to allow the sample to flow into the sample concentrator. The sample concentrator uses a water management system to remove water while minimally affecting the target substances, then passes the sample into the concentration step. The water management system takes several minutes to cycle, and that delays the injection of the sample. While this type of system, which is the current state of the art, is successful, the dilution/pressurization step takes time and introduces the possibility of error. Dilution of the sample has a negative effect on system sensitivity. The water management system operation adds several minutes to the time required for each analysis.
Additionally, spacecraft designers are required to recover and remove carbon dioxide from the cabin air, and they need to recover drinking water from all waste streams. The presence of high levels of humidity in the air detracts from the ability of some carbon dioxide removal systems to work at peak efficiency. Additionally, water can be difficult and/or energy expensive to remove from waste while providing sufficient purity for re-use as drinking water.
Additionally, persons working or living, whether in the military or in civilian capacity, in locations with limited availability of potable water have a need to be able to recover potable water from a plurality of sources of nonpotable or toxic or contaminated moisture, including from human waste. Many types of systems for providing potable water are either heavy and require substantial energy input, or have substantial limitations on the types of contamination for which they work properly.
Additionally, water samples collected for analysis often contain trace levels of toxic substances. The analysis of water samples often requires the extraction from the water and subsequent concentration of those trace toxic substances for the analysis to be performed. There is a partition coefficient between the water sample and the extraction medium that sets a lower limit of concentration of the trace toxic substance below which the quantitative nature of the extraction is substantially less than complete, and the accuracy of the analysis is affected detrimentally.